1. Field of the Invention
The present invention relates to a quartz resonator which suppresses harmonic vibration of a lower order (or overtone vibration). The present invention relates to, in particular, a harmonic vibration of a lower order suppressing quartz resonator wherein a value obtained by adding 1 to a ratio of value Q (Q.sub.1) of a main-electrode section to value Q (Q.sub.2) of a sub-electrode section is defined as suppression degree, the gap between a main-electrode and a sub-electrode is determined using the suppression degree and harmonic vibration of a lower order is thereby lowered to below the oscillation limit of an oscillation circuit.
2. Background of the Invention
Conventionally, a quartz resonator has been widely used from communications equipment to industrial equipment to household equipment. This is because the quartz resonator has characteristics of, for example, small size, high frequency stability and accuracy. In recent years, harmonic (or overtone) quartz resonator has been used more frequently since operation frequency becomes higher in mobile communications, and the clock frequency of computers becomes higher.
To obtain desired high frequency vibration using a harmonic quartz resonator, it is necessary to give special consideration such as providing coils to the circuits so as not to cause harmonic (including a fundamental wave) vibration of a lower order than desired order of harmonic vibration to generate oscillation and setting a circuit constant to a special value.
For purposes of improving such inconvenience mentioned above, there have been proposed several types of harmonic quartz resonators which suppress the resonance response of harmonic vibration of a lower order. One of the inventors of the present invention has indicated, as disclosed in Japanese Patent Application Publication No. 4-76527, providing sub electrodes on both sides of the vicinity of a main electrode with gaps between them, determining the gap appropriately to thereby sufficiently contain the vibration energy of the desired harmonic vibration within the main electrode, and propagating the vibration energy of harmonic vibration of a lower order through the gap to the sub electrode side as a traveling wave to thereby suppress the resonance response of the harmonic vibration of a lower order.
In the vibrator which suppresses a harmonic vibration of a lower order as stated above, however, if sub electrodes arranged on both sides of the vicinity of the main electrode are small to make the quartz resonator smaller in size, the harmonic (including fundamental wave) vibration of a lower order is insufficiently suppressed. In order to sufficiently suppress the vibration of a lower order at the desired frequency, a prototype of the vibrator has to be repeatedly made and many steps and high costs are required to obtain necessary data for the suppression of the harmonic vibration of a lower order.